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 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package javax.swing.text;

import java.util.Vector;
import java.awt.*;
import javax.swing.event.*;

/**
 * ZoneView is a View implementation that creates zones for which
 * the child views are not created or stored until they are needed
 * for display or model/view translations.  This enables a substantial
 * reduction in memory consumption for situations where the model
 * being represented is very large, by building view objects only for
 * the region being actively viewed/edited.  The size of the children
 * can be estimated in some way, or calculated asynchronously with
 * only the result being saved.
 * <p>
 * ZoneView extends BoxView to provide a box that implements
 * zones for its children.  The zones are special View implementations
 * (the children of an instance of this class) that represent only a
 * portion of the model that an instance of ZoneView is responsible
 * for.  The zones don't create child views until an attempt is made
 * to display them. A box shaped view is well suited to this because:
 * <ul>
 * <li>
 * Boxes are a heavily used view, and having a box that
 * provides this behavior gives substantial opportunity
 * to plug the behavior into a view hierarchy from the
 * view factory.
 * <li>
 * Boxes are tiled in one direction, so it is easy to
 * divide them into zones in a reliable way.
 * <li>
 * Boxes typically have a simple relationship to the model (i.e. they
 * create child views that directly represent the child elements).
 * <li>
 * Boxes are easier to estimate the size of than some other shapes.
 * </ul>
 * <p>
 * The default behavior is controlled by two properties, maxZoneSize
 * and maxZonesLoaded.  Setting maxZoneSize to Integer.MAX_VALUE would
 * have the effect of causing only one zone to be created.  This would
 * effectively turn the view into an implementation of the decorator
 * pattern.  Setting maxZonesLoaded to a value of Integer.MAX_VALUE would
 * cause zones to never be unloaded.  For simplicity, zones are created on
 * boundaries represented by the child elements of the element the view is
 * responsible for.  The zones can be any View implementation, but the
 * default implementation is based upon AsyncBoxView which supports fairly
 * large zones efficiently.
 *
 * @author Timothy Prinzing
 * @see View
 * @since 1.3
 */
public class ZoneView extends BoxView {

  int maxZoneSize = 8 * 1024;
  int maxZonesLoaded = 3;
  Vector<View> loadedZones;

  /**
   * Constructs a ZoneView.
   *
   * @param elem the element this view is responsible for
   * @param axis either View.X_AXIS or View.Y_AXIS
   */
  public ZoneView(Element elem, int axis) {
    super(elem, axis);
    loadedZones = new Vector<View>();
  }

  /**
   * Get the current maximum zone size.
   */
  public int getMaximumZoneSize() {
    return maxZoneSize;
  }

  /**
   * Set the desired maximum zone size.  A
   * zone may get larger than this size if
   * a single child view is larger than this
   * size since zones are formed on child view
   * boundaries.
   *
   * @param size the number of characters the zone may represent before attempting to break the zone
   * into a smaller size.
   */
  public void setMaximumZoneSize(int size) {
    maxZoneSize = size;
  }

  /**
   * Get the current setting of the number of zones
   * allowed to be loaded at the same time.
   */
  public int getMaxZonesLoaded() {
    return maxZonesLoaded;
  }

  /**
   * Sets the current setting of the number of zones
   * allowed to be loaded at the same time. This will throw an
   * <code>IllegalArgumentException</code> if <code>mzl</code> is less
   * than 1.
   *
   * @param mzl the desired maximum number of zones to be actively loaded, must be greater than 0
   * @throws IllegalArgumentException if <code>mzl</code> is &lt; 1
   */
  public void setMaxZonesLoaded(int mzl) {
    if (mzl < 1) {
      throw new IllegalArgumentException("ZoneView.setMaxZonesLoaded must be greater than 0.");
    }
    maxZonesLoaded = mzl;
    unloadOldZones();
  }

  /**
   * Called by a zone when it gets loaded.  This happens when
   * an attempt is made to display or perform a model/view
   * translation on a zone that was in an unloaded state.
   * This is implemented to check if the maximum number of
   * zones was reached and to unload the oldest zone if so.
   *
   * @param zone the child view that was just loaded.
   */
  protected void zoneWasLoaded(View zone) {
    //System.out.println("loading: " + zone.getStartOffset() + "," + zone.getEndOffset());
    loadedZones.addElement(zone);
    unloadOldZones();
  }

  void unloadOldZones() {
    while (loadedZones.size() > getMaxZonesLoaded()) {
      View zone = loadedZones.elementAt(0);
      loadedZones.removeElementAt(0);
      unloadZone(zone);
    }
  }

  /**
   * Unload a zone (Convert the zone to its memory saving state).
   * The zones are expected to represent a subset of the
   * child elements of the element this view is responsible for.
   * Therefore, the default implementation is to simple remove
   * all the children.
   *
   * @param zone the child view desired to be set to an unloaded state.
   */
  protected void unloadZone(View zone) {
    //System.out.println("unloading: " + zone.getStartOffset() + "," + zone.getEndOffset());
    zone.removeAll();
  }

  /**
   * Determine if a zone is in the loaded state.
   * The zones are expected to represent a subset of the
   * child elements of the element this view is responsible for.
   * Therefore, the default implementation is to return
   * true if the view has children.
   */
  protected boolean isZoneLoaded(View zone) {
    return (zone.getViewCount() > 0);
  }

  /**
   * Create a view to represent a zone for the given
   * range within the model (which should be within
   * the range of this objects responsibility).  This
   * is called by the zone management logic to create
   * new zones.  Subclasses can provide a different
   * implementation for a zone by changing this method.
   *
   * @param p0 the start of the desired zone.  This should be &gt;= getStartOffset() and &lt;
   * getEndOffset().  This value should also be &lt; p1.
   * @param p1 the end of the desired zone.  This should be &gt; getStartOffset() and &lt;=
   * getEndOffset().  This value should also be &gt; p0.
   */
  protected View createZone(int p0, int p1) {
    Document doc = getDocument();
    View zone;
    try {
      zone = new Zone(getElement(),
          doc.createPosition(p0),
          doc.createPosition(p1));
    } catch (BadLocationException ble) {
      // this should puke in some way.
      throw new StateInvariantError(ble.getMessage());
    }
    return zone;
  }

  /**
   * Loads all of the children to initialize the view.
   * This is called by the <code>setParent</code> method.
   * This is reimplemented to not load any children directly
   * (as they are created by the zones).  This method creates
   * the initial set of zones.  Zones don't actually get
   * populated however until an attempt is made to display
   * them or to do model/view coordinate translation.
   *
   * @param f the view factory
   */
  protected void loadChildren(ViewFactory f) {
    // build the first zone.
    Document doc = getDocument();
    int offs0 = getStartOffset();
    int offs1 = getEndOffset();
    append(createZone(offs0, offs1));
    handleInsert(offs0, offs1 - offs0);
  }

  /**
   * Returns the child view index representing the given position in
   * the model.
   *
   * @param pos the position &gt;= 0
   * @return index of the view representing the given position, or -1 if no view represents that
   * position
   */
  protected int getViewIndexAtPosition(int pos) {
    // PENDING(prinz) this could be done as a binary
    // search, and probably should be.
    int n = getViewCount();
    if (pos == getEndOffset()) {
      return n - 1;
    }
    for (int i = 0; i < n; i++) {
      View v = getView(i);
      if (pos >= v.getStartOffset() &&
          pos < v.getEndOffset()) {
        return i;
      }
    }
    return -1;
  }

  void handleInsert(int pos, int length) {
    int index = getViewIndex(pos, Position.Bias.Forward);
    View v = getView(index);
    int offs0 = v.getStartOffset();
    int offs1 = v.getEndOffset();
    if ((offs1 - offs0) > maxZoneSize) {
      splitZone(index, offs0, offs1);
    }
  }

  void handleRemove(int pos, int length) {
    // IMPLEMENT
  }

  /**
   * Break up the zone at the given index into pieces
   * of an acceptable size.
   */
  void splitZone(int index, int offs0, int offs1) {
    // divide the old zone into a new set of bins
    Element elem = getElement();
    Document doc = elem.getDocument();
    Vector<View> zones = new Vector<View>();
    int offs = offs0;
    do {
      offs0 = offs;
      offs = Math.min(getDesiredZoneEnd(offs0), offs1);
      zones.addElement(createZone(offs0, offs));
    } while (offs < offs1);
    View oldZone = getView(index);
    View[] newZones = new View[zones.size()];
    zones.copyInto(newZones);
    replace(index, 1, newZones);
  }

  /**
   * Returns the zone position to use for the
   * end of a zone that starts at the given
   * position.  By default this returns something
   * close to half the max zone size.
   */
  int getDesiredZoneEnd(int pos) {
    Element elem = getElement();
    int index = elem.getElementIndex(pos + (maxZoneSize / 2));
    Element child = elem.getElement(index);
    int offs0 = child.getStartOffset();
    int offs1 = child.getEndOffset();
    if ((offs1 - pos) > maxZoneSize) {
      if (offs0 > pos) {
        return offs0;
      }
    }
    return offs1;
  }

  // ---- View methods ----------------------------------------------------

  /**
   * The superclass behavior will try to update the child views
   * which is not desired in this case, since the children are
   * zones and not directly effected by the changes to the
   * associated element.  This is reimplemented to do nothing
   * and return false.
   */
  protected boolean updateChildren(DocumentEvent.ElementChange ec,
      DocumentEvent e, ViewFactory f) {
    return false;
  }

  /**
   * Gives notification that something was inserted into the document
   * in a location that this view is responsible for.  This is largely
   * delegated to the superclass, but is reimplemented to update the
   * relevant zone (i.e. determine if a zone needs to be split into a
   * set of 2 or more zones).
   *
   * @param changes the change information from the associated document
   * @param a the current allocation of the view
   * @param f the factory to use to rebuild if the view has children
   * @see View#insertUpdate
   */
  public void insertUpdate(DocumentEvent changes, Shape a, ViewFactory f) {
    handleInsert(changes.getOffset(), changes.getLength());
    super.insertUpdate(changes, a, f);
  }

  /**
   * Gives notification that something was removed from the document
   * in a location that this view is responsible for.  This is largely
   * delegated to the superclass, but is reimplemented to update the
   * relevant zones (i.e. determine if zones need to be removed or
   * joined with another zone).
   *
   * @param changes the change information from the associated document
   * @param a the current allocation of the view
   * @param f the factory to use to rebuild if the view has children
   * @see View#removeUpdate
   */
  public void removeUpdate(DocumentEvent changes, Shape a, ViewFactory f) {
    handleRemove(changes.getOffset(), changes.getLength());
    super.removeUpdate(changes, a, f);
  }

  /**
   * Internally created view that has the purpose of holding
   * the views that represent the children of the ZoneView
   * that have been arranged in a zone.
   */
  class Zone extends AsyncBoxView {

    private Position start;
    private Position end;

    public Zone(Element elem, Position start, Position end) {
      super(elem, ZoneView.this.getAxis());
      this.start = start;
      this.end = end;
    }

    /**
     * Creates the child views and populates the
     * zone with them.  This is done by translating
     * the positions to child element index locations
     * and building views to those elements.  If the
     * zone is already loaded, this does nothing.
     */
    public void load() {
      if (!isLoaded()) {
        setEstimatedMajorSpan(true);
        Element e = getElement();
        ViewFactory f = getViewFactory();
        int index0 = e.getElementIndex(getStartOffset());
        int index1 = e.getElementIndex(getEndOffset());
        View[] added = new View[index1 - index0 + 1];
        for (int i = index0; i <= index1; i++) {
          added[i - index0] = f.create(e.getElement(i));
        }
        replace(0, 0, added);

        zoneWasLoaded(this);
      }
    }

    /**
     * Removes the child views and returns to a
     * state of unloaded.
     */
    public void unload() {
      setEstimatedMajorSpan(true);
      removeAll();
    }

    /**
     * Determines if the zone is in the loaded state
     * or not.
     */
    public boolean isLoaded() {
      return (getViewCount() != 0);
    }

    /**
     * This method is reimplemented to not build the children
     * since the children are created when the zone is loaded
     * rather then when it is placed in the view hierarchy.
     * The major span is estimated at this point by building
     * the first child (but not storing it), and calling
     * setEstimatedMajorSpan(true) followed by setSpan for
     * the major axis with the estimated span.
     */
    protected void loadChildren(ViewFactory f) {
      // mark the major span as estimated
      setEstimatedMajorSpan(true);

      // estimate the span
      Element elem = getElement();
      int index0 = elem.getElementIndex(getStartOffset());
      int index1 = elem.getElementIndex(getEndOffset());
      int nChildren = index1 - index0;

      // replace this with something real
      //setSpan(getMajorAxis(), nChildren * 10);

      View first = f.create(elem.getElement(index0));
      first.setParent(this);
      float w = first.getPreferredSpan(X_AXIS);
      float h = first.getPreferredSpan(Y_AXIS);
      if (getMajorAxis() == X_AXIS) {
        w *= nChildren;
      } else {
        h += nChildren;
      }

      setSize(w, h);
    }

    /**
     * Publish the changes in preferences upward to the parent
     * view.
     * <p>
     * This is reimplemented to stop the superclass behavior
     * if the zone has not yet been loaded.  If the zone is
     * unloaded for example, the last seen major span is the
     * best estimate and a calculated span for no children
     * is undesirable.
     */
    protected void flushRequirementChanges() {
      if (isLoaded()) {
        super.flushRequirementChanges();
      }
    }

    /**
     * Returns the child view index representing the given position in
     * the model.  Since the zone contains a cluster of the overall
     * set of child elements, we can determine the index fairly
     * quickly from the model by subtracting the index of the
     * start offset from the index of the position given.
     *
     * @param pos the position >= 0
     * @return index of the view representing the given position, or -1 if no view represents that
     * position
     * @since 1.3
     */
    public int getViewIndex(int pos, Position.Bias b) {
      boolean isBackward = (b == Position.Bias.Backward);
      pos = (isBackward) ? Math.max(0, pos - 1) : pos;
      Element elem = getElement();
      int index1 = elem.getElementIndex(pos);
      int index0 = elem.getElementIndex(getStartOffset());
      return index1 - index0;
    }

    protected boolean updateChildren(DocumentEvent.ElementChange ec,
        DocumentEvent e, ViewFactory f) {
      // the structure of this element changed.
      Element[] removedElems = ec.getChildrenRemoved();
      Element[] addedElems = ec.getChildrenAdded();
      Element elem = getElement();
      int index0 = elem.getElementIndex(getStartOffset());
      int index1 = elem.getElementIndex(getEndOffset() - 1);
      int index = ec.getIndex();
      if ((index >= index0) && (index <= index1)) {
        // The change is in this zone
        int replaceIndex = index - index0;
        int nadd = Math.min(index1 - index0 + 1, addedElems.length);
        int nremove = Math.min(index1 - index0 + 1, removedElems.length);
        View[] added = new View[nadd];
        for (int i = 0; i < nadd; i++) {
          added[i] = f.create(addedElems[i]);
        }
        replace(replaceIndex, nremove, added);
      }
      return true;
    }

    // --- View methods ----------------------------------

    /**
     * Fetches the attributes to use when rendering.  This view
     * isn't directly responsible for an element so it returns
     * the outer classes attributes.
     */
    public AttributeSet getAttributes() {
      return ZoneView.this.getAttributes();
    }

    /**
     * Renders using the given rendering surface and area on that
     * surface.  This is implemented to load the zone if its not
     * already loaded, and then perform the superclass behavior.
     *
     * @param g the rendering surface to use
     * @param a the allocated region to render into
     * @see View#paint
     */
    public void paint(Graphics g, Shape a) {
      load();
      super.paint(g, a);
    }

    /**
     * Provides a mapping from the view coordinate space to the logical
     * coordinate space of the model.  This is implemented to first
     * make sure the zone is loaded before providing the superclass
     * behavior.
     *
     * @param x x coordinate of the view location to convert >= 0
     * @param y y coordinate of the view location to convert >= 0
     * @param a the allocated region to render into
     * @return the location within the model that best represents the given point in the view >= 0
     * @see View#viewToModel
     */
    public int viewToModel(float x, float y, Shape a, Position.Bias[] bias) {
      load();
      return super.viewToModel(x, y, a, bias);
    }

    /**
     * Provides a mapping from the document model coordinate space
     * to the coordinate space of the view mapped to it.  This is
     * implemented to provide the superclass behavior after first
     * making sure the zone is loaded (The zone must be loaded to
     * make this calculation).
     *
     * @param pos the position to convert
     * @param a the allocated region to render into
     * @return the bounding box of the given position
     * @throws BadLocationException if the given position does not represent a valid location in the
     * associated document
     * @see View#modelToView
     */
    public Shape modelToView(int pos, Shape a, Position.Bias b) throws BadLocationException {
      load();
      return super.modelToView(pos, a, b);
    }

    /**
     * Start of the zones range.
     *
     * @see View#getStartOffset
     */
    public int getStartOffset() {
      return start.getOffset();
    }

    /**
     * End of the zones range.
     */
    public int getEndOffset() {
      return end.getOffset();
    }

    /**
     * Gives notification that something was inserted into
     * the document in a location that this view is responsible for.
     * If the zone has been loaded, the superclass behavior is
     * invoked, otherwise this does nothing.
     *
     * @param e the change information from the associated document
     * @param a the current allocation of the view
     * @param f the factory to use to rebuild if the view has children
     * @see View#insertUpdate
     */
    public void insertUpdate(DocumentEvent e, Shape a, ViewFactory f) {
      if (isLoaded()) {
        super.insertUpdate(e, a, f);
      }
    }

    /**
     * Gives notification that something was removed from the document
     * in a location that this view is responsible for.
     * If the zone has been loaded, the superclass behavior is
     * invoked, otherwise this does nothing.
     *
     * @param e the change information from the associated document
     * @param a the current allocation of the view
     * @param f the factory to use to rebuild if the view has children
     * @see View#removeUpdate
     */
    public void removeUpdate(DocumentEvent e, Shape a, ViewFactory f) {
      if (isLoaded()) {
        super.removeUpdate(e, a, f);
      }
    }

    /**
     * Gives notification from the document that attributes were changed
     * in a location that this view is responsible for.
     * If the zone has been loaded, the superclass behavior is
     * invoked, otherwise this does nothing.
     *
     * @param e the change information from the associated document
     * @param a the current allocation of the view
     * @param f the factory to use to rebuild if the view has children
     * @see View#removeUpdate
     */
    public void changedUpdate(DocumentEvent e, Shape a, ViewFactory f) {
      if (isLoaded()) {
        super.changedUpdate(e, a, f);
      }
    }

  }
}
